The present invention relates to the freeing of seized valves and in particular, but not exclusively, to the freeing of seized water valves.
Flow control valves, particularly for controlling the flow of water, are frequently left completely undisturbed in the same position for extended periods of time, sometimes as long as tens of years. The valves may remain in a fully closed or fully open position or in an intermediate position between the two extremes.
When such valves are not regularly actuated it is common for scale to be deposited on the internal components of the valve. The build-up of scale can be so severe that it becomes impossible to actuate the valve, particularly if the valve has not been actuated for many years. The problem occurs with all types of valves including, for example, gate valves, plug valves, ball valves, check valves and butterfly valves.
When it becomes necessary to actuate the valve (for example to isolate a length of pipe to permit repair work to be carried out downstream of the valve) if the valve has become irreversibly stuck by build-up of scale the only solution is to locate an operable valve upstream of the seized valve, close the upstream valve and remove and replace the seized valve. Not only can this inconvenience consumers who might otherwise have retained a normal supply if the seized valve had been operable, but the replacement of the seized valve is a time-consuming and expensive procedure. Moreover, it is rare that the replaced valve can be renovated and it is usually scrapped.
It is an object of the present invention to provide a method of freeing seized valves.
In accordance with a first aspect of the present invention, there is provided a method of freeing a seized valve of the type having a valve housing, an inlet, an outlet, a valve seat within the valve housing between the inlet and the outlet and a valve closure member releasably engageable with the valve seat to control the degree of opening of the valve, the method comprising:
(a) forming one or more injection ports in the wall of the valve housing adjacent to the seized portions of the valve;
(b) injecting a pressurised treatment fluid towards the seized portions of the valve through the or each injection port; and
(c) closing off the or each port.
This has been found to free seized valves very effectively and normally obviates the need for removal and replacement of the seized valve.
In one embodiment, the invention further comprises the steps of:
(d) forming an inspection port in a wall of the valve housing; and
(e) determining the location of the seized portions of the valve via the inspection port.
Preferably, the location of the seized portions of the valve is determined by investigation of the interior of the valve via the inspection port. The location of the seized portions can be determined visually and/or by means of a probe.
Preferably, wherein, prior to step (b), a pressurised test fluid is applied to the or each injection port to ensure that the port is suitable for undergoing step (b). This ensures that a potentially catastrophic build-up of pressure does not occur when the treatment fluid is injected.
Preferably, the treatment fluid is an anti-scale fluid. It may be a lubricant, with a high cone penetration, e.g. a lubricant in the form of a solid to semisolid dispersion of a thickening agent in a fluid lubricant, such as a grease. The fluid is preferably insoluble in the fluid whose flow the valve is designed to control.
Optionally, the method further comprises inducing vibration in at least a portion of the valve where seizure has occurred.
The vibration frees seized valves very effectively and normally obviates the need for removal and replacement of the seized valve. The technique is particularly useful for dislodging build-ups of scale deposits which are often responsible for seizure of valves.
It has been found that induction of vibration at ultrasonic frequencies is particularly effective. The vibration may be induced by placing an ultrasonic transducer in contact with a portion of the valve (e.g. a valve housing or an internal component of the valve such as a threaded stem or a valve closure gate of a gate valve). Alternatively, or in addition, the vibration may be induced by placing the transducer in contact with a liquid which is itself in contact with a portion of the valve. In particular, the transducer may be passed through an aperture in a valve housing so that it projects into liquid enclosed within the housing.
The vibration of the liquid causes so-called xe2x80x9ccavitationxe2x80x9d or xe2x80x9ccold boilingxe2x80x9d of the liquid, which results in rapid formation and implosion of bubbles within the fluid. It is the cavitation of the liquid which is thought to dislodge build-ups of scale deposits.
In accordance with a second aspect of the present invention, a composition for freeing seized valves comprises by weight:
75-90% (preferably 80-85%) polyalphaolefins
3-15% (preferably 6-12%) powdered silica
0.5-5% (preferably 1.5-3%) powdered PTFE
1-6% (preferably 2-5%) di-n-octyl sebecate.
Preferably the composition further comprises a bacteriocide which may, for example, comprise 0.05-1% (and preferably 0.1-0.5%) by weight of the composition.
Preferably the composition further comprises an antioxidant which may, for example, comprise 0.05-1% (and preferably 0.1-0.5%) by weight of the composition.
The present invention also includes a method of freeing a seized valve in accordance with the first aspect, wherein the treatment fluid comprises a composition in accordance with the second aspect.
In accordance with a third aspect of the present invention, there is provided a valve comprising a valve housing, an inlet, an outlet, a valve seat between the inlet and the outlet, a valve closure member releasably engageable with the valve seat to control the degree of opening of the valve and a plurality of ports in a wall of the valve housing at locations where seizure of the valve is anticipated to occur.
If such a valve were to seize at some time in the future, the method of freeing the valve would be simplified, in view of the fact that most, if not all, of the necessary ports would already have been provided on the valve during manufacture. The ports are preferably tapped and would be plugged during normal use of the valve.